1. Field of the Invention
The present invention relates in general to a welding technique applied to aluminum alloy members, and more particularly to a filler wire for laser-welding aluminum alloy members, a method for welding the aluminum alloy members by using the filler wire and a welded aluminum alloy member produced by using the filler wire.
2. Description of the Related Art
In road motor vehicles, reduction in weight of the vehicle body is one of the effective measures to achieve an improved fuel efficiency. In view of this, in place of the conventionally used steel, usage of aluminum alloy members as the vehicle body has been frequently attempted in these days. Furthermore, in order to reduce the cost of the aluminum alloy-produced vehicle body and improve the productivity of the same, some parts of them, such as couplings for the space frame, B-pillars and the like, have been produced of aluminum alloy die castings through a vacuum die casting method. For uniting these aluminum alloy parts, arc welding (such as MIG (metal inert gas) welding or the like), laser welding and riveting have been usually employed. When uniting the aluminum alloy parts is carried out by using the MIG welding or the laser welding wherein a high density energy is used as a heat source, generation of undesired blowholes (viz., porosity) tends to easily occur as compared with a case of uniting steel parts. Of course, presence of such blowholes lowers the mechanical strength and ductility of the welded portions of the aluminum alloy parts.
It has been revealed that most of the blowholes originates from hydrogen gas produced during the welding. This is because when being melted, the aluminum alloy shows a high solubility or holding ability to hydrogen, and such hydrogen solubility of the alloy lowers as the temperature lowers.
Furthermore, due to inevitability possessed by the production method, the aluminum alloy die casting parts have a marked amount of air contained therein. When the aluminum alloy die casting parts are subjected to welding, the air in the parts is forced to escape therefrom, which causes easy generation of the blowholes as compared with a case wherein the welding is applied to aluminum alloy parts produced through an extrusion method.
In order to restrain and reduce generation of such blowholes in the welded portions of the aluminum alloy die casting parts, optimization of welding conditions, such as cleaning the portions to be welded, finding an optimum welding speed and an optimum flow rate of shielding gas and the like, has been hitherto carried out. In addition to this, the amount of gas led into the parts during the production process has been severely controlled.
However, the above-mentioned optimization of welding conditions tends to sacrifice the productivity of the vehicle body due to the prime needing with which the quality of the welded portions is considered. Furthermore, in order to control the gas amount in the aluminum alloy die casting parts, very skilled and thus costly technique is needed for assuring the quality of the die casting parts. In fact, hitherto, solving the above-mentioned shortcomings has been one major theme in the field of welding technique of aluminum alloy parts.
The theme on the above-mentioned blowhole generation brings about a similar theme in another field where the surface of an aluminum alloy part is refined by using, as a heat source, MIG arcing or electron beam irradiation which has a high density energy. In this field, as a welding material that can suppress generation of blowholes in case of carrying out the surface refining of the aluminum alloy part, Japanese Patent First Provisional Publication 6-304780 shows a welding aluminum wire (viz., filler wire) which contains therein 0.1 to 8 wt. % of a flux which comprises 5 to 10% of sodium (Na), 40 to 45% of potassium (K), less than 5% of oxygen (O), less than 5% of sulfur (S), 5 to 10% of fluorine (F) and 35 to 40% of chlorine (Cl). Furthermore, Japanese Patent First Provisional Publication 7-96396 shows an aluminum filler material for welding, which contains 0.05 to 20 wt. % of C2Cl6 in powder form. However, even these publications provide substantially no description about a filler wire which exhibits a sufficient control effect against generation of the blowholes during welding of the aluminum alloy die casting parts.
In view of the above-mentioned task, one object of the present invention is to provide a filler wire used for welding aluminum alloy parts, particularly for welding aluminum alloy die casting parts, which can sufficiently control or restrain generation of the undesired blowholes during welding of them.
Another object of the present invention is to provide a method for welding aluminum alloy die casting parts by using such filler wire.
Still another object of the present invention is to provide a welded-aluminum alloy part made by using the filler wire.
According to a first aspect of the present invention, there is provided a filler wire for laser-welding an aluminum alloy, which comprises a base material; and a flux of Alxe2x80x94Kxe2x80x94F (viz., Aluminum-potassium-fluorine)-based composition, wherein the amount of the flux in the base material is greater than 0 (zero) wt. % and less than approximately 1.0 wt. %.
According to a second aspect of the present invention, there is provided a method of welding a work piece of aluminum alloy, which comprises preparing a work piece of aluminum alloy; and laser-welding the work piece by using a filler wire, the filler wire comprising a base material and a flux of Alxe2x80x94Kxe2x80x94F (viz., Aluminum-potassium-fluorine)-based composition, the amount of the flux in the base material being greater than 0 (zero) wt. % and less than approximately 1.0 wt. %.
According to a third aspect of the present invention, there is provided a welded-aluminum alloy member which is produced by the process comprising the steps of preparing an aluminum alloy; and laser-welding the aluminum alloy by using a filler wire, the filler wire comprising a base material and a flux of Alxe2x80x94Kxe2x80x94F (viz., Aluminum-potassium-fluorine)-based composition, the amount of the flux in the base material being greater than 0 (zero) wt. % and less than approximately 1.0 wt. %.